Generally, regenerative fluid machines have a simpler structure than typical centrifugal or axial-flow fluid machines, and have excellent durability as well as features appropriate to obtain a large head at a relatively small flow rate. Such regenerative fluid machines have been applied to vehicle fuel pumps, industrial high-pressure air blowers, or air blowers for fuel cells that requires high pressure, and research on decreasing size and increasing pumping efficiency has been conducted. In particular, regenerative fluid machines are known as ring blowers in the air blower field, and problems of such a conventional ring blower will be described.
FIG. 1 is an exploded perspective view illustrating an example of a conventional ring blower, and FIG. 2 is a cross-sectional view illustrating an assembled state of FIG. 1. As illustrated in FIGS. 1 and 2, a conventional ring blower has a structure in which a circular plate-shaped impeller 10 is installed in a pair of casings 20. The impeller 10 has a plurality of vanes 12 that are radially formed on outer circumferences of both faces thereof at regular intervals, and impeller grooves 14 are formed between the vanes 12. The impeller 10 is rotatably driven by a motor (not shown).
Further, ring-shaped flow channels 30 facing the impeller grooves 14 are provided inside the pair of casings 20, respectively. Each of the flow channels 30 forms a separate flow field. Alternatively, there is also a structure in which the impeller grooves 14 are formed only in one face of the impeller 10, and thus one flow channel 30 is provided. Furthermore, both ends of each flow channel 30 are provided with a suction hole 32 and a discharge hole 34.
In the ring blower having such a configuration, as the impeller 10 rotates, a gas is introduced through the suction holes 32 of the flow channels 30, and a high-pressure gas which circulates between the impeller grooves 14 and the flow channels 30 to accumulate energy is discharged through the discharge holes 34.
In order to improve performance of the regenerative fluid machine such as the ring blower, it is necessary to accurately understand a flow characteristic of the fluid to prevent pumping efficiency from being degraded due to energy loss. To this end, the concept of a relative velocity will be introduced, and the flow characteristic in the regenerative fluid machine will be examined.
FIG. 3 is a diagram for describing a flow characteristic of a fluid in flow channels and impeller grooves. A plurality of small arrows shown in FIG. 3 represent velocity vectors according to a flow of the fluid. Thus, as the impeller 10 rotates clockwise, a circulation flow is shown in which the fluid is introduced from the flow channels 30 into the impeller grooves 14, flows outside the impeller grooves 14, and returns to the flow channels 30 again. Such a circulation flow is repeatedly formed in the plurality of impeller grooves 14 and the flow channels 30, thereby increasing pressure of the fluid.
A large arrow shown in FIG. 3 briefly illustrates the circulation flow obtained by introducing the concept of the relative velocity. A symbol Va represents an absolute velocity of the fluid that is introduced from the flow channels 30 into the impeller grooves 14, and a symbol Vb represents a velocity of the impeller 10 that rotates clockwise. Furthermore, a symbol Vc represents a relative velocity of the fluid that is introduced into the impeller grooves 14 and on which relative rotation of the impeller 10 is reflected. In this case, the absolute velocity Va and the relative velocity Vc of the fluid have an absolute inflow angle α and a relative inflow angle β with respect to the velocity Vb of the impeller 10.
Meanwhile, as in FIG. 3, the relative inflow angle β of the fluid has a different vane angle than the impeller vanes 12. As such, this difference generates eddies in the impeller grooves 14. Accordingly, there is a problem in that energy loss caused by the eddies remarkably reduces the pumping efficiency of the regenerative fluid machine. In this case, it can be seen that, as the difference between the relative inflow angle β at which the fluid is introduced into the impeller grooves 14 and the vane angle of the vanes 12 increases, the energy loss caused by the eddies becomes greater.
Accordingly, the fluid is introduced into the impeller grooves 14 in a state in which the relative inflow angle β of the fluid is increased, in other words, in which a direction of the relative velocity Vc of the fluid is set to be parallel to the vanes 12. Thereby, the generation of the eddies can be minimized, and performance of the regenerative fluid machine can be improved.
However, improvement of the performance of the conventional regenerative fluid machine has mainly focused on improving shapes of the vanes 12 and the impeller grooves 14 in the impeller 10. For this reason, it is increasingly difficult to fabricate the shape of the impeller 10, and manufacturing costs are increased.
In addition, in the conventional regenerative fluid machine, since the impeller 10 is designed without properly conducting research on the flow characteristics of the fluid, the improvement of the performance of the regenerative fluid machine is limited.